Cell-Based 'Tracking Devices' Might Help Monitor Treatments

TUESDAY July 10, 2012 -- Call it a fantastic voyage. Scientists have successfully found a way to inject tiny iron filings into the human body to potentially monitor medical therapies. The particles work as tracking devices that may help physicians determine if certain treatments are working.

The development of methods to track cells is critical to stem-cell and other therapies that rely on the delivery of particular cells to a target site, such as the heart or other organ, according to the authors of a small new study.

"Eventually we'll be able to prove stem cells are going where they are supposed to be and track cells going into other tissues," said Dr. David Newby, study co-author and professor and chair of cardiology at the Centre for Cardiovascular Science at the University of Edinburgh, in Scotland.

The study, published July 10 in Circulation: Cardiovascular Imaging, showed that immune cells tagged with nano-sized iron filings and injected into the bloodstream can be tracked by magnetic resonance imaging (MRI) as they move through the human body. The researchers also demonstrated that the process was safe and did not interfere with normal cell function.

A type of normal white blood cell known as macrophages ingest pathogens and cellular debris -- including the filings -- and take them along wherever they go. The iron filings are only about 20 nanometers across. In comparison, the average red blood cell is 8,000 nanometers wide.

Newby said the critical question the researchers wanted to answer was whether the tracking cells, once injected into the body, would migrate where the researchers wanted them to go. "We needed to be able to know if they wander off," he said.

The research showed it is possible to track tagged, injected cells for seven days. Because MRI technology is nonradioactive, the tracking system would not subject patients to radiation exposure, Newby noted.

The study involved two phases. First, the researchers determined that blood cells with attached iron filings moved normally, and were indeed able to survive. Twenty study volunteers participated. Some people were given injections into their thigh muscles of either unlabeled cells, iron-filing labeled cells or just the filings. Others received intravenous injections of the labeled blood cells.

To show that the tracking method could be used to facilitate the development of cell-based therapies in the future, the researchers injected one person with labeled immune blood cells, and they tracked the cells as they migrated to an inflamed area of skin on the thigh. The inflammation was caused by a Mantoux tuberculosis test, an injection just under the skin that typically becomes slightly inflamed.

"This is a pretty convincing demonstration that there's real merit to this idea of using cells as carriers," said Matthew Tirrell, a professor and Pritzker director of the Institute for Molecular Engineering, at the University of Chicago.

Tirrell said the research opens up new territory for other kinds of visualization experiments. "There are few examples of any kind of targeting particles in humans," he said. "To have the confidence and guts to do it is impressive, and I think other people will be building on this work," he said.

Newby said that the research team hopes to investigate the use of these techniques to diagnose inflammatory conditions of the heart, such as transplant rejection, myocarditis or inflammation of the heart, and sarcoidosis, where there is inflammation in multiple organs. The work may also be useful in five to 10 years in stem-cell research, he added.

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